Relationship between the viscosity and the performance of submucosal injection materials

Viscous submucosal injection materials (SIMs) such as sodium hyaluronate that are widely used in endoscopic treatments for early gastrointestinal cancer and polyps contribute to the treatment outcomes. Although viscosity can be measured in a relatively simple way, the relationship between the SIM performances [such as injection pressure (IP) and submucosal elevation height (SEH)] and the viscosity has not been evaluated. This study aimed to analyze this relationship and elucidate whether it is possible to predict the SIM performances by viscosity measurements, and to identify the optimum viscosity characteristics for high-performance SIMs. Viscosity, IP, and SEH of conventional and developing SIMs were measured, and the correlation between these values was evaluated. SEH was measured with a ex vivo model using porcine stomach specimen. The magnitude of IP increased as the endoscopic injection needle gauge, injection speed, and concentration of SIM were increased. The strongest correlations were observed between viscosity at higher shear rate and IP and between viscosity at lower shear rate and SEH. This study identified the viscosities that represent the SIM characteristics. These findings will contribute to the design and accelerate the development of suitable high-performance SIM by eliminating complex characterization methods. The pseudoplastic-based SIMs whose viscosity decreases as the shear rate increases are estimated to have higher performance SIMs based on this study.